Hydraulic transmission with pressurized reservoir



April 18, 1950 Y J. K. DOUGLAS 2,504,665

HYDRAULIC TRANSMISSION WITH PRESSURIZED RESERVOIR Filed July 1, 1948 2Sheets-Sheet 1 'l/lllllllllllll/llllllllim v ITIIIIIIIIIIIII 1 3OIIIIIIIIIIIIIIIIII i 5 z 6/ I z 7 I 2 s 35 35 a l' I 34 2 I f F E-[III/11111111111/1111/1/1111i11/11111111/11/11/1/1/1/1111/1/ INVENTORJAMES K. DOUGLAS Y ATTORNEY P 8, 1950 J. K. DOUGLAS I 2,504,663

' HYEiRAULIC TRANSMISSION WITH PRESSURIZED RESERVOIR Filed July 1, 1948a V w 2 Sheets-Sheet '2 I 'l/l/I/ I I N q S 3| f r m N N N z 2 s I 5 NEn 3 5 IO & s I! x I, v 8 I, r- Q l ml 1 r ml 0 3 a I 1 I r n I IIIIIIIIIIIIIIII'IIII j L I JI 2/ E f I m I I Lu I n i 1." if: p i l 5 92 m ll/l/l/l/l/Il/l/ II/IllIII/l/l E N o z a N t I f" S m Q- N N i v i i v Iu a (O x z a z z y INVENTOR JAMES K. DOUGLAS ATTORNEY Patented Apr. 18,1950 UNITED STATES PATENT OFFICE HYDRAULIC TRANSMISSION WITH PRESSURIZEDRESERVOIR Application July 1, 1948, Serial No. 36,400

11 Claims.

This invention relates to hydraulic transmissions of the type whichincludes a hydraulic motor, a pump for supplying motive liquid to themotor to effect operation thereof, a reservoir containing a supply ofliquid for the pump, means connecting the pump and the motor into ahydraulic circuit and means for reversing the flow in the circuit tocause the motor to operate in opposite directions alternately, and inwhich the motor is so constructed that during operation thereof in onedirection the liquid discharged therefrom is in excess of the liquidrequired to supply the pump and that during operation of the motor inthe opposite direction the liquid discharged therefrom is less than theliquid required to supply the pump.

For example, the transmission may be of the type which includes adifferential reciprocating motor, such as a cylinder having a pistonfitted therein and provided with a piston rod which extends through oneend only of the cylinder, and a valve for directing liquid from the pumpto the rod end of the cylinder and from the head end of the cylinder tothe pump and to the reservoir to eiiect operation of the motor in onedirection and for directing liquid from the pump and liquid from the rodend of the cylinder to the head end of the cylinder to efiect operationof the motor in the opposite direction. For the purpose of illustration,the invention will be explained as embodied in a transmission of thistype but it is to be understood that the invention is applicable toother types of transmissions.

When the pump delivers liquid to the rod end of the motor cylinder, thehead end of the cylinder is connected to the intake of the pump andthe-liquid delivered by the pump causes the motor "piston to move towardthe head end of the cylinder and to expel liquid from the cylinder tothe intake of the pump. Due to the displacement of the piston rod, theliquid expelled from the cylinder is in excess of the liquid required tosupply the pump and the excess liquid is exhausted through a backpressure valve into the reservoir.

when the pump delivers liquid to the head end of the motor cylinder, theends or the cylinder are connected to each other. The liquid deliveredby the pump causes the motor piston to move toward the rod end of thecylinder and to expel liquid therefrom to the head end of the cylinderso that at this time the pump m-ust draw its entire supply of liquidfrom the reservoir through a suitable suction valve. The level of theliquid in the reservoir thus rises and falls during each reciprocationof the motor piston.

It is well known that the motive liquid must I be kept as free aspossible from bubbles of air or gas as bubbles in the liquid causes themotor piston to slow down in response to an increase in load and to jumpahead in response to a suddent decrease in load. Theoretically, thejoints in the suction valve and the associated parts may be madeairtight but it has been found in practice that the joints do not remainairtight and that air seeps through the joints and becomes entrained inthe motive liquid during the time that the pump is sucking its supply ofliquid from the reservoir. Also, the liquid employed in suchtransmissions is a mineral oil and, when a pump is sucking oil from alower level, the pressure at the intake of the pump is below atmosphericpressure which causes gas bubbles to form in the oil.

The present invention has as an object to prevent air from entering themotive liquid through the suction valve assembly.

Another object is to supercharge the pump during at least the greaterpart of the time that the transmission is in operation.

Other and more specific objects will appear from the followingdescription of the embodiment of the invention shown schematically inthe accompanying drawings in which the views are as follows:

Fig. l is a diagram of the hydraulic circuit of a transmission in whichthe invention is embodied, the flow of liquid to effect movement of themotor piston toward the left being indicated by arrows.

Fig. 2 is a view similar to Fig. 1 but indicating the flow of liquid toeffect movement of the motor piston toward the right.

Fig. 3 is a diagrammatic view showing the pump mounted upon thereservoir in the customary manner, the reservoir being shown in verticallongitudinal section and the pump being shown in elevation with a partthereof shown in section and with certain channels shown in positionsdifferent from those occupied in actual practice.

As shown, the transmission includes a hydraulic motor I having a piston2 fitted in a stationary cylinder 3 and provided with a piston rod 4which extends through one end of cylinder 3 for connection to an elementto be reciprocated such as the table of a bed planer.

Liquid for energizing motor I is supplied by a pump 5 which is mounteddirectly upon reserapoaeoa voir 8 and when the drive is in operation itis The flow of liquid to and from motor I is controlled by a valve 1which in practice is mounted upon reservoir 6 at the right 01' pump 5 inrespect to Fig. 3 and which is connected to opposite ends of pump 5 bytwo channels 8 and 9 and is connected to opposite ends of cylinder 3 bytwo channels and ii.

Valve 1 has been indicated as being of a well known type of diiierentialcontrol valve which either will connect opposite sides of pump toopposite ends of cylinder 3 as indicated in Fig. 1 or will connect theoutlet of pump 5 and the rod end of cylinder 3 to the head end ofcylinder 3 as indicated in Fig. 2 but the valve used in practice is a socalled combination valve which includes a start and stop valve, adirection control valve and a pilot valve and which is similar to thevalve shown in Patent No. 1,943,061 except that the control valve isarranged for differential operation of the motor as explained above.-Also, pump 5 has been shown as being a unidirectional pump which has itsoutput directed to one end or the other of cylinder 3 by valve I but thesame result may be obtained by using a reversible pump; and connecting asimple differential valve be-, tween the pump and the motor as shown inPatent No. 2,093,690.

The intake side of pump 5 communicates through a channel [4 with theoutlet of a suction valve l5 which is attached to the bottom of the pumpcasing and extends downward through an opening l6 formed in the upperwall of reservoir 6. The inlet of suction valve l5 has a suction pipe 11connected thereto and extending downward to a point near the bottom ofreservoir 6.

The intake side of pump 5 also communicates through a channel ill withthe inlet of a low pressure resistance valve, l9 which functions as aback pressure valve and has its outlet connected by..a channel to a pipe2| which extends downward through opening it to a point near the bottomof reservoir 6 and then extends laterally so that liquid dischargedthrough pipe 2| will enter reservoir 6 at points remote from suctionpipe IT. The pressure created by pump 5 is limited by high pressurerelief valve 22 which has its inlet connected to the discharge side ofpump 5 and its outlet connected by a channel 23 to the intake of pump 5.

Assuming that the hydraulic circuit is filled with liquid, that pump 5is running and that ther is an adequate supply of liquid in reservoir 6,the transmission will operate as follows:

When valve I connects opposite sides of pump 5 to opposite ends ofcylinder 3 as indicated in Fig. 1, liquid from pump 5 will flow throughchannel 8, valve 1 and channel Hi to the rod end of cylinder 3 and movepiston 2 toward the left on a working stroke. Piston 2 will eject liquidfrom the head end of cylinder 3 through channel ii, valve 1 and channel8 to the intake of pump 5. Due to the displacement of rod 4, the liquidejected from cylinder 3 is in excess of the liquid required to supplypump 5 so that all of the ejected liquid cannot enter pump 5 which willcause pressure to rise and open back pressure valve is and then theexcess liquid will flow through valve iii, channel 20 and pipe 2| intoreservoir 6. Back pressure valve l9 thus causes back pressure to bemaintained upon piston 2 and causes pump 5 to be supercharged at thatpressure.

When valve I connects the outlet of pump 5 and the rod end of cylinder 3to the head end of cylinder 3 as indicated in Fig. 2, pump 5 will drawliquid from reservoir 8 through pipe ll, valve l5 and channel I and willdischarge it through channel =8, valve 1 and channel H to the head endof cylinder 3 and thereby cause piston 2 to move toward the right on anidle stroke and to eject liquid from the rod end of cylinder 3 throughchannel l0, valve I and channel ii to the head end of cylinder 3 so thatno liquid is returned to pump 5 which, therefore, must suck its entiresupply of liquid from reservoir 3.

The suction valve assembly may be made as air tight as possible such asby inserting'gaskets between the parts thereof and between the valvecasing and the casing of. pump 5 but it will not remain air tight and,consequently, when pump 5 sucks its supply of liquid from reservoir 6,air will seep through the joints of the suction valve assembly and beentrained in the liquid unless means are provided to prevent it.

seepage of air through the suction valve joints is prevented by keepingthe suction valve submerged in liquid. This is accomplished by arrangingthe suction valve in a separate chamber and utilizing the flow of liquidinto and out oi reservoir 6 to keep the level of the liquid in thatchamber above the suction valve.

Reservoir 3 is made as nearly air tight as possible as by welding itsjoints, by arranging suitable gaskets between its walls and the coverswhich close such access openings as may be necessary to provide adequateaccess to the interior of reservoir 6, and by arranging a suitablegasket 25 around opening l5 between the bottom of pump 5 and the topwall of reservoir 6, the thicknesses of the gaskets being exaggerated inthe drawing.

Suction valve I5 is arranged within a suction chamber 25 formed by acontinuous imperforate wall 26 which extends around opening is and hasits lower end spaced a short distance above the bottom of reservoir 6and its upper end joined as by welding to the top wall of reservoir 6 toform a fiuidtight joint therewith.

In order that the flow of liquid into and out of reservoir 6 may beutilized to keep suction valve i5 submerged in liquid, a small airtighttank 30 is arranged within reservoir 6 outward from chamber 25. Tank 30is connected as by means of a branched channel 3| to the outlets of twocheck valves 32 and 33 and by means of a channel 34 to the inlet of acheck valve 35 which opens into reservoir 5. The inlet of check valve 32communicates with the atmosphere as by being connected to a channel 36which extends through the top wall of reservoir 6 and forms a fiuidtightjoint therewith. The inlet of check valve 33 is connected by a channel31 to the suction chamber at a point above suction valve 15. In theparticular pump shown-in Fig. 3, channel 31 extends through wall 26,being welded thereto to form a fiuidtight joint therewith, and thenextends upward into a pocket 38 which is formed in the casing of pump 5and communicates with the interior of suction chamber 25.

Reservoir 6 is made large enough to leave a substantial air space abovethe liquid when the volume of liquid therein is maximum, that is, whenpiston 2 is at the extreme end of its movement toward the left, and thevolume of liquid supplied to reservoir '6 is great enough to maintainthe liquid level above the lower end of suction chamber 25 when thevolume of liquid in the reservoir is at its minimum, that is, whenpiston 2 is at the extreme end of its movement toward the right.

Assuming that piston 2 stopped at the end of its movement toward theleft, that pump is running and that the level of the liquid in suctionchamber 25 is the same as the level of the liquid in reservoir 5,suction valve l5 will become submerged and kept submerged in thefollowing manner:

When pump 5 draws liquid from reservoir 5 and delivers it to motor I toeffect an idle stroke thereof as explained above and as indicated inFig. 2, the resultant decrease in the volume of liquid in reservoir Iwill reduce the pressure in the air space which will cause air to flowthrough channel 35, check valve 32, channel ll, tank 30, channel 34 andcheck valve 35 into reservoir 5 to fill the space occupied by the liquidwithdrawn by pump 5.

Then when liquid flows into reservoir 5 during the working stroke ofpiston 2 as explained above and as indicated in Fig. l, the incomingliquid will compress the air in the air space for the reason that aircannot escape from reservoir 5 due to the check valves. The pressurecreated by the incoming liquid will cause liquid to rise in suctionchamber 25 and to expel air from the upper part thereof through channel31, check valve 33 and channel 3| into tank 30 and create a low pressuretherein. Also, any air or gas in the incoming liquid will rise into theair space for the reason that pipe 2| discharges the liquid at pointsoutside of suction chamber 25.

Due to the pressure in tank 30, air will escape therefrom throughchannel 34 and check valve 35 into reservoir 5 the next time pump 5draws liquid from reservoir 5, thereby preventing the pressure in theair space from dropping below atmospheric pressure. As the level of theliquid in reservoir 6 drops due to pump 5 drawing liquid therefrom, thelevel of the liquid in suction chamber 25 will start to drop but itcannot drop very far for the reason that the upper end of chamber 25 issealed.

The liquid in chamber 25 may not be raised above suction valve l5 duringthe first cycle of operations in which case the liquid will be raisedprogressively higher each time liquid flows into reservoir 6 untilchamber 25 is substantially filled with liquid and thereafter'liquidand/or air will be expelled from chamber 25 through channel 31, checkvalve 33 and channel 3| into tank 30 each time liquid flows intoreservoir 6.

Suction valve I5 is thus kept submerged so that air cannot seep throughits joints into the motive liquid. Also, any air or gas bubbles in thehydraulic circuit will be expelled therefrom in a very short time due tothe incoming liquid being discharged into reservoir 5 at points spacedfrom suction chamber 25.

After piston 2 has made one or more reciprocations, the liquid forcedinto reservoir *5 during each succeeding movement of piston 2 toward theleft will create pressure in reservoir 5 and in tank 30 as explainedabove and, during the latter part of each movement of piston 2 towardthe left, the pressure in reservoir 5 and in tank 30 will be increasedabove the pressure required to raise liquid to the top of suctionchamber 25. Then when valve 1 is shifted to cause piston 2 to movetoward the right as indicated in Fig. 2, the pressure in reservoir 5 andin tank 30 will force liquid through valve l5 into the intake of pump 5until suflicient liquid has been expelled from reservoir 5 to drop thepressure therein below that required to raise liquid into the pumpintake.

Pump 5 is thussupercharged at a low pressure during the first part ofthe idle stroke of piston 2 and it must reduce the pressure at itsintake below atmospheric pressure only during the latter part of thestroke at which time the pressure at the pump intake need not be reducedas much below atmospheric pressure as would be necessary if suctionchamber 25 were not kept substantially filled with liquid at all times.Consequently, gasiflcation of the liquid entering the pump is reduced toa minimum.

The invention has thus far been explained as applied to a transmissionhaving a circuit in which no liquid is returned from the motor to thepump during operation of the motor in one direction. I

However, the invention is equally applicable to a transmission having acircuit in which liquid is returned from the motor to the pump duringoperation of the motor in both directions but the rate at which liquidis returned to the pump during operation of the motor in one directionis less than the rate of pump delivery.

For example, if valve 1 were an ordinary reversing valve instead of adifferential valve, the flow of liquid during movement of piston 2toward the left would be the same as indicated in Fig. 1 but, duringmovement of piston 2 toward the right, pump 5 would deliver liquid tothe head end of cylinder 3 and it would have liquid returned to it fromthe rod end of cylinder 3 at a in the opposite direction. Consequently,the pressurized reservoir would function in exactly the same way ineither circuit.

The pressurized reservoir may also be employed in a transmission themotor of which has two piston rods of different diameters fixed toopposite ends of its piston and extending through opposite ends of itscylinder" or which consists of two single acting cylinders havingseparate rams. In either case, the pressurized reservoir would functionin the manner described above except.

that the volume of liquid flowing into and out of the reservoir would beequal to the difference between the displacements of the two piston rodsor the two rams.

It is to be noted that in the transmissions de scribed but notillustrated herein the valve may be omitted and a. reversible pumpsubstituted for the unidirectional pump.

The invention herein set forth is susceptible of various othermodifications and adaptations without departing from the scope of theinvention which is hereby claimed as follows:

1. In a hydraulic transmission of the type which includes a reservoir ofliquid, a pump having extending from the bottom thereof a suction valvethrough which said pump may be supplied with liquid from said reservoir,a hydraulic motor and means for directing liquid from said pump to saidmotor to cause it to perform successive cycles of operation, and saidmotoris so constructed that during one part of each of said cycles theliquid discharged from said motor is in excess of pump requirements andthe excess liquid is discharged into said reservoir and during the otherpart of each of said cycles the liquid discharged from said motor isless than pump requirements and said pump must draw liquid through saidvalve from said reservoir so that liquid flows into and out of saidreservoir during each of said cycles, the combination with said pump ofa fluidtight reservoir containing a supply of liquid and fastened to thebottom of said pump to form a fluidtight joint therewith, a suctionchamber having fluidtight side walls arranged within said reservoiraround said suction valve and connected to the bottom of said pump toform a fluidtight joint therewith, said chame ber having the lower endthereof open and arranged below the lowest level of liquid in saidreservoir, and means responsive to the flow of liquid into and out ofsaid reservoir for raising the .level of the liquid in said chamberabove said suction valve.

2. In a hydraulic transmission of the type which includes a reservoir ofliquid, 2. pump having extending from the bottom thereof a suction valvethrough which said pump may be supplied with liquid from said reservoir,a hydraulic motor and means for directing liquid from said pump to saidmotor to cause it to perform successive cycles of operations, and saidmotor is so constructed that during one part of each of said cycles theliquid discharged from said motor is in excess of pump requirements andthe excess liquid is discharged into said reservoir and during the otherpart of each of said cycles the liquid discharged from said motor isless than pump requirements and said pump must draw liquid through saidvalve from said reservoir so that liquid flows into and out of saidreservoir during each of said cycles, the combination with said pump ofa reservoir adapted to contain a supply of liquid and fastened to thebottom of said pump to form a fluidtight joint therewith, said reservoirbeing constructed to prevent escape of fluid therefrom except throughsaid suction valve, a suction chamber having fluidtight side wallsarranged within said reservoir around said suction valve and connectedto the bottom of said pump to form a fluidtight joint therewith, saidchamber having the lower end thereof open and arranged below the lowestlevelrof liquid in said reservoir, a channel extending from the upperpart of said chamber into said reservoir, a check valve in said channelto permit fluid to escape from said chamber but preventing flow in theopposite direction, and means connected to said channel and responsiveto flow of liquid into and out of said reservoir for creating sufiicientpres sure in said reservoir during said inflow of liquid to raise thelevel of the liquid in said chamber above the level of the liquid insaid reservoir outside said chamber and thereby cause fluid to flow fromsaid chamber through said check valve so that after the level of theliquid in said chamber has been raised a substantial distance above saidsuction valve said suction valve will remain submerged in liquid duringcontinued operation of said pump.

3. In a hydraulic transmission of the type which includes a reservoir ofliquid, a pump having extending from the bottom thereof a suction valvethrough which said pump may be supplied with liquid from said reservoir,a hy- 8 said pump to said motor to cause it to perform successive cyclesof operations, and said motor is so constructed that during one part ofeach of said cycles the liquid discharged from said motor is in excessof pump requirements and the excess liquid is discharged into saidreservoir and duringvthe other part of each of said cycles the liquiddischarged from said motor is less than pump requirements and said pumpmust draw liquid through said valve from said reservoir so that liquidflows into and out of said reservoir during each of said cycles, thecombination with said pump of a reservoir adapted to contain a supply ofliquid and fastened to the bottom of said pump to form a fluidtightjoint therewith, said reservoir being constructed to prevent escape offluid therefrom except through said suction valve, a suction chamberhaving fluidtight side walls arranged within said-reservoir around saidsuction valve and connected to the bottom of said pump to form afluidtight Joint therewith, said chamber having the lower end thereofopen and arranged below the lowest level of liquid in said reservoir, achannel extending from the upper part of said chamber into saidreservoir, a check valve in said channel to permit fluid to escape fromsaid chamber but preventing flow in the opposite direction, meansconnected to said channel and responsive to flow of liquid into and outof said reservoir for creating sufiicient pressure in said reservoirduring said inflow of liquid to raise the level of the liquid in saidchamber above the level of the liquid in said reservoir outside saidchamber and thereby cause fluid to flow from said chamber through saidcheck valve so that after the level of the liquid in said chamber hasbeen raised a substantial distance above said suction valve said suctionvalve will remain submerged in liquid during continued operation of saidpump, and an exhaust channel communicating with the intake of said pumpand extending to a point below said suction valve.

4, In a hydraulic transmission of the type which includes a reservoir ofliquid, a pump having extending from the bottom thereof a suction valvethrough which said pump may be supplied with liquid from said reservoir,a hydraulic motor and means for directing liquid from said pump to saidmotor to cause it to perform successive cycles of operations, and saidmotor is so constructed that during one part of each of said cycles theliquid discharged from said motor is in excess of pump requirements andthe excess liquid is discharged into said reservoir and during the otherpart of each of said cycles the liquid discharged from said motor isless than pump requirements and said pump must draw liquid through saidvalve from said reservoir so that liquid flows into and out of saidreservoir during each of said cycles, the combination with said pump ofa reservoir adapted to contain a supply of liquid and fastened to thebottom of said pump to form a fluidtight joint therewith, said reservoirbeing constructed to prevent escape of fluid therefrom except throughsaid suction valve, a suction chamber having fluidtight side wallsarranged within said reservoir around said suction valve and connectedto the bottom of said pump to form a fluidtight joint therewith, saidchamber having the lower end thereof open and arranged below the lowestlevel of liquid in said reservoir, a channel extending from the draulicmotor and means for directing liquid from '7 upper part of said chamberinto said reservoir,

escape from said chamber but preventing flow in the opposite direction,means connected to said channel and responsive to flow of liquid intoand out of said reservoir for creating suilicient pressure in saidreservoir during said inflow of liquid to raise the level'of the liquidin said chamber above the level of the liquid in said reservoir outsidesaid chamber and thereby cause fluid to flow from said chamber throughsaid check valve so that after the level of the liquid in said chamberhas been raiseda substantial distance above said suction valve saidsuction valve will remain submerged in liquid during continued operationof said pump, and an exhaust channel communicating with the intake ofsaid pump and extending into said reservoir a substantial distancelaterally outward from said suction chamber.

5. In a hydraulic transmisison of the type which includes a reservoir ofliquid, a pump having extending from the bottom thereof a suction valvethrough which said pump may be sup- :plied with-liquid fromsaidreservoir, a hydraulic motor and means for directing liquid fromsaid 'pump to said motorto cause it to perform suc- --ing the other partof each of said cycles the liquid discharged from said motor is lessthan pump requirements and said pump must draw liquid through said valvefrom said reservoir so that liquid flows into and out of said reservoirduring each of said cycles, the combination with said pump of areservoir adapted to contain a supply of liquid and fastened to thebottom of said pump to form afiuidtight joint therewith, a suctionchamber having fiuidtight side walls arranged within said reservoiraround said suction valve and connected to the bottom of said pump toform a fiuidtight joint therewith,

said chamber having the lower end thereof 'open and arranged below thelowest level of 7/ liquid in said reservoir, a small tank arrangedwithin said reservoir close to the top thereof and outside saidchamber,-a check valve opening from said tank into said reservoir, acheck valve opening from the top of said chamber into said tank, a checkvalve opening from the atmosphere into said tank, said reservoir andsaid tank being fiuidtight-except -for said check valves, and an exhaustchannel communicating with the intake of said pump and extending intosaid reservoir a substantial distance laterally outward from saidsuction chamber.

6. In a hydraulic transmission oi the type which includes a reservoir ofliquid, a pump having a suction valve and a channel connecting saidvalve to the intake of said pump, a hydraulic motor and means fordirecting liquid from said pump to said motor to cause it to performsuccessive cycles of operations, and said motor is so constructed thatduring one part of each of said cycles the liquid discharged from saidmotor is in excess of pump requirements and the excess liquid isdischarged into said reservoir and during the other part of each of saidcycles the liquid discharged from said motor is less than pumprequirements and said pump must draw liquid through said valve from saidreservoir so that liquid flows into and out of said reservoir duringeach of said cycles, the combination with said a check valve in saidchannel to permit fluid to I pump of a fiuidtight reservoir containing asup ply of liquid arranged around said suction valve and forming afiuidtight joint around said channel, a suction chamber havingfiuidtight side walls arranged within said reservoir around said suctionvalve and forming a fiuidtight joint around said channel, said chamberhaving the lower. end thereof open and arranged below the lowest levelof liquid in said reservoir, and means responsive to the flow of liquidinto and out of said reservoir for raising the level of the liquid insaid suction chamber above said suction valve.

7. In a hydraulic transmission of the type which includes a reservoir ofliquid, a pump having a suction valve and a channel connecting saidvalve to the intake of said pump, a hydraulic motor and means fordirecting liquid from said pump to said motor to cause it to performsuccessive cycles of operations, and said motor is so constructed thatduring one part of each of said cycles the liquid discharged from saidmotor is in excess of pump requirements and the excess liquid isdischarged into said reservoir and during the other part of each of saidcycles the liquid discharged from said motor is less than pumprequirements and said pump must draw liquid through said valve from saidreservoir so that liquid flows into and out of said reservoir duringeach of said cycles, the combination with said pump of a fiuidtightreservoir containing a supply of liquid arranged around said suctionvalve and forming a fiuidtight joint around said channel, a suctionchamber having fiuidtight side walls arranged within said reservoiraround said suction valve and forming a fiuidtight joint around saidchannel, said chamber having the lower end thereofppen and arrangedbelow the lowest level of liquid in said reservoir, a fiuidtight storagecompartment, and means for permitting fluid to flow from outside saidreservoir or from the upper part of said suction chamber into saidstorage compartment and from said compartment into said reservoir butpreventing flow in the opposite direction.

8. In a hydraulic transmission of the type which includes a reservoir ofliquid, a pump having a suction valve and a channel connecting saidvalve to the intake of said pump, a hydraulic motor and means fordirecting liquid from said pump to said motor to cause it to performsuccessive cycles of operations, and said motor is so constructed thatduring one part of each of said cycles the liquid discharged from saidmotor is in excess of pump requirements and the excess liquid isdischarged into said reservoir and during the other part of each of saidcycles the liquid discharged from said motor is less than pumprequirements and said pump must draw liquid through said valve from saidreservoir so that liquid flows into and out of said reservoir duringeach of said cycles, the combination with said pump of a fiuidtightreservoir containing a supply of liquid arranged around said suctionvalve and forming a fiuidtight joint around said channel, a suctionchamber having fiuidtight side walls arranged within said reservoiraround said suction valve and forming a fiuidtight joint around saidchannel, said chamber having the lower end thereof open and arrangedbelow the lowest level of liquid in said reservoir, a tank arrangedwithin said reservoir outside said chamber, a check valve opening fromsaid tank into said reservoir, a check valve opening from the top ofsaid chamber into .said tank, and a check valve opening from theatmosphere into said tank, said reser- 11 voir and said tank beingfluidtight except for" 'each of said cycles the liquid discharged fromsaid motor is less than pump requirements and said pump must draw liquidthrough said valve from said reservoir so that liquid flows into and outof said reservoir during each of said cycles, the combination with saidpump of a fluid tight reservoir containing a supply of liquid arrangedaround said suction valve and forming a fluidtight joint around saidchannel, a suction chamber having fluidtight side walls arranged withinsaid reservoir: around said suction valve and forming a fluidtight jointaround said channel, said chamber having the lower end thereof open andarranged below the lowest level of liquid in said reservoir, a tankarranged within said reservoir outside said chamber, a, check valveopening from said tank into said reservoir, a check valve opening fromthe top of said chamber into said tank, a check valve opening from theatmosphere into said tank, said reservoir and said tank being fluidtightexcept for said check valves, and an exhaust channel communicating withthe intake of said pump and extending to a point below said suctionvalve.

10. In a hydraulic transmission of the type which includes a reservoirof liquid, a pump having a suction valve and a channel connecting saidvalve to the intake of said'pump, a hydraulic motor and means fordirecting liquid from said pump to said motor to cause it to performsuecessive cycles of operations, and said motor is so constructed thatduring one part of each of said cycles the liquid discharged from saidmotor is in excess of pump requirements and the excess liquid isdischarged into said reservoir and during the other part of each of saidcycles the liquid discharged from said motor is less than pumprequirements and said pump must draw liquid or liquid arranged aroundsaid suction valve and forming a fluidtight joint around said channel. asuction chamber having fluidtight side walls arranged within saidreservoir'around said suction valve and forming a fluidtight jointaround said channel, said chamber having the lower end thereof open andarranged below the lowest level of liquid in said reservoir, a tankarranged within said reservoir outside said chamber, a check valveopening from said tank into said reservoir, 2. check valve opening fromthe top of said chamber into said tank, a check valve opening from theatmosphere into said tank, said reservoir and said tank being fluidtightexcept for said check valves; and an exhaust channel communicating withthe intake of said pump and extending into said reservoir a substantialdistance laterally outward from said suction chamber.

11. In a hydraulic transmission of the type which includes a reservoirof liquid, a pump having a suction valve and a channel connecting saidvalve to the intake of said pump, a hydraulic motor and means fordirecting liquid from said pump to said motor to cause it to performsuccessive cycles of operations, and said motor is so constructed thatduring one part of each of said cycles the liquid discharged from saidmotor is in excess of pump requirements and the excess liquid isdischarged into said reservoir and during the other part of each of saidcycles the liquid discharged from said motor is less than pumprequirements and said pump must draw liquid through said valve from saidreservoir so that liquid flows into and out of said reservoir duringeach of said cycles, the combination with said pump of a fluidtightreservoir containing a supply of liquid arranged around said suctionvalve and forming a fluidtight joint around said channel, a suctionchamber having fluidtight side walls arranged within said reservoiraround said suction valve and forming a fluidtight joint around saidchannel, said chamber having the lower end thereof open and arrangedbelow the lowest level of liquid in said reservoir, a small tankarranged within said reservoir close to the top thereof and outside saidchamber, a check valve opening from said tank into said reservoir, 2.check valve openingfrom the top of said chamber into said tank, and acheck valve opening from the atmosphere into said tank, said reservoirand said tank being fluidtight except for said check valves. 7

JAMES K. DOUGLAS.

No references cited.

